Process of electroplating on tungsten



Patented June 22, 1948 PROCESS OF ELECTBOPLATING ON TUNGSTEN Joseph J.Cannizzaro, Baltimore, Md., assignor to Westinghouse ElectricCorporation, East Pittsburgh,'Pa., a corporation of Pennsylvania Q NoDrawing. Application December 5, 1944,

Serial No. 566,775 7 v 3 Claims.

1 This invention relates to the plating of a metal upon tungstenmembers, and more particularly to the electroplating of a metal onvarious hing-- sten members in the form of wire, sheets and the like. i

Previously the electroplating of metals on tungsten has not beensatisfactory from the standpoint of an adherent bond between the metaland the tungsten. Tungsten wire, in particular, has not beenelectroplated heretofore satisfactorily with other metals. Even with thebest of care, in the prior art practice an electroplated coating ofmetal deposited on tungsten wire can be readily stripped off in the formof a tubular sheath. This indicates that the bond between theelectroplated metal and the tungsten is ineffective for producing astrongly united composite member.

For many applications, it is desirable to produce a tenaciously adherentelectroplated coating of some metal on tungsten sheets, wires and otherbodies of the tungsten. For example, it may be desirable to soft soldera tungsten wire or the like to a base composed of copper or other metal.Tungsten, however, is not considered to be soft solderable. However, anelectroplated coating of nickel on the tungsten will permit effectivesoft soldering to be accomplished. Numerous other applications arefacilitated if an electroplated coating of some metal, such as nickel,copper, tin or the like, can be electroplated on the tungsten with agood adherent bond being present.

The object of this invention is to provide an adherent electroplatedcoating of a metal on tungsten members.

A further object of the invention is to pro vide for etching tungstenmembers to facilitate electroplating thereon of adherent coatings ofmetals.

Other objects of the invention will in part be obvious and will in partbe apparent hereafter.

It has been discovered that tungsten may be electroetched to provide fora clean surface having such characteristics that metals may beelectroplated thereon to produce tenaciously adherent coatings. Briefly,the electroetching process consists in applying to the tungsten memberan aqueous solution containing from 5% to 50% hydrofluoric acid andwhile the tung sten member is in contact with the aqueous solution ofhydrofluoric acid applying alternating current at a voltage of the orderof 5 volts. The current is conducted to the'solution through a secondelectrode composed of platinum, graphite or other relatively inertmaterial. The etch ing is accomplished at room temperature though thesolution may be heated, if desired. The operation may be accomplishedrapidly, generally a period of time of one or two minutes beingsuflicient. V

As anexample of the practice of the invention, a tungsten wire wasconnected to alternating current at 5 volts and immersed in a bathcontaining 24% hydrofluoric acid solution, the other electrode in thiscase being ofplatinum. After one minute at room temperature, thetungsten wire was found to be etched to a clean bright state suitablefor electroplating a metal thereon. The etched wire was immediatelytransferred to a conventional nickel plating solution containing nickelchloride and sulfate salts. A direct current of milliamperes at 6 voltswas applied to the etched tungsten wire while in the plating solution.In one minute, a thin coating of nickel was plated upon the tungstenwire.

The nickel plated tungsten wire was bent sharply several times andotherwise mechanically deformed without any observable loosening orcracking of the nickel plated coating. By comparison, a, tungsten wirenot subjected to the electroetch of this invention but cleaned bydipping in a mineral acid and then electroplated in the same nickelsolution acquired a relatively non-adherent nickel coating. Upon bendingthe latter wire, the nickel plated coating sleeved and could be readilyremoved from the wire.

The electroetched tungsten may be plated in any of the conventionalplating solutions such, for example, as copper, tin, zinc, chromium,cadmium and the like. It is desirable to commence plating of theelectroetched tungsten wire as soon as possible after removal from theetching bath in order to prevent the reoxidation of the cleaned tungstensurfaces. The thickness of plating may be varied to suit requirements.Since the bond between the clean tungsten and electroplated metal isextremely adherent the plated member may be subjected to varioustreatment without failure. The electroplated tungsten members may bemechanically processed by bending, swaging, twisting or other desiredtreat-- ment. Likewise the electroplated tungsten members may be heatedin order to accomplish soldering or to produce any predeterminedcondition in the composite member.

The nickel plated tungsten wire whose making was above described indetail was satisfactorily bent to predetermined shapeand soldered to acopper base member for use in producing a crystal probe. The tungstenwire could not be satisfactorily welded or hard soldered to the basemember, since overheating would take place and the tungsten wire wouldbe unsatisfactory for its intendedpurpose,

Since certain "changes may be made in the above invention and differentembodiments of the invention may be made without departing. from thescope thereof, it is intended that all matter contained in the abovedisclosure shall be interpreted as illustrative and not in a limitingsense.

I claim as my invention:

1. In the process of electroplating a metal. on a tungsten member, thesteps comprising applying to the tungsten member a hydrofluoric acidsolution, passing an alternating current at 5 volts through the tungstenmember in the presence of the hydrofluoric acid solution for from one totwo minutes to etch the surface, removing the etched tungsten memberfrom the hydrofluoric acid solution and electroplating a metal on thetreated tungstenmem-ber.

2. In the process of electroplating a metal on a tungsten member, thesteps comprising applying. to the tungsten member an aqueous solution.having from 5% to 50% hydrofluoric acid, passing an alternatingcurrentat 5 volts through the tungsten member while it is in contactwith the aqueous solution for a period of time to etch the surface ofthe member, removing the tungsten member from the aqueous solution andelectroplating a metal on the treated member.

3. In the process of plating nickel on a tungsten member, the stepscomprising, applying to the tungsten. member an aqueous solution havingfrom 5'% to- 50% hydrofluoric acid, passing an alternating current at 5volts through the tungsten member while it is in contact with theaqueous solution for a period of from one to two minutes to etch themember, removing the tungsten member from the aqueous solution, applyingto the tungsten member a plating solution from which nickel may beelectro-deposited, passing a direct current through the member and theplating solution to plate nickel on the tungsten member.

JOSEPH J. CANNIZZARO.

REFERENCES CITED The following referencesare of record in the file of"this patent:

UNITED STATES PATENTS OTHER REFERENCES Websters New InternationalDictionary, 22nd ed. 1940,.pages 171-5 and 1716.

